1. Field of the Invention
The present invention relates to a method of injecting lubricant into a space between the outside of double-wall pipes and the ground and laying a conduit comprised of double-wall pipes each of which comprises an inner pipe and an outer pipe by propelling the double-wall pipes, and to a method of injecting filler into a space formed between inner pipes and outer pipes, after the conduit has been laid.
2. Description of the Prior Art
Laying sewer conduit or service water conduit in the ground is carried out by tunneling through the ground by a tunneling machine, while the tunneling machine followed by pipes such as Hume pipes and steel pipes are propelled by a pipe-jacking machine, wherein it is carried out to inject lubricant into a space between the outside of the tunneling machine and the ground and between the outside of pipes and the ground. Further, in the above-mentioned pipe-jacking method; it is also carried out to inject back-filling material into a space between the outside of pipes forming a conduit and the ground, after having laid the conduit.
Each pipe, with diameters over 800mm, used in the above-mentioned pipe-jacking method is formed with a hole at a given position. The hole is connected through a hose with a lubricant or a back-filling material feeder, which is provided on the ground. While propelling the pipes, lubricant is injected into a space between the outside of the pipes and the ground, by supplying lubricant through the hose to the hole and injecting lubricant to into the space through the hole so that frictional force can be decreased, or after having laid a desired conduit in the ground, back-filling material is injected into a space between the outside of the pipes and the ground so that the space between the outside of the pipes and the ground is filled with back-filling material.
On the other hand, there are cases where a conduit for supplying gas, such as coal gas or fuel gas and natural gas and others is laid in the ground. Since a gas pipe requires the highest gas tightness, gas pipes are connected to each other by mutually welding the edges of pipes, wherein the weld is inspected by non-destructive inspection to form a conduit for supplying gas without welding defects is formed.
Since a gas pipe requires the highest gas tightness, it is thought that a gas pipe cannot be provided with a hole for injecting lubricant or back-filling material into a space between the outside of the pipes and the ground. Further, it is thought that the edge of a gas pipe cannot be brought into immediate contact with a push ring of a pipe-jacking machine so that gas pipes cannot be propelled by a pipe-jacking machine, because there is the possibility that the edge of the gas pipe will be damaged by the push ring.
Since there are the above-mentioned problems, when laying a conduit for gas, a conduit comprised of Hume pipes with the diameter sufficiently larger than the outside of the gas pipe is first laid by the pipe-jacking method, and a space between the outside of the conduit comprised of Hume pipes and the ground is filled with back-filling material, then a conduit for gas supply comprised of the gas pipes is formed within the conduit comprised of Hume pipes.
Recently, it was developed that double-wall pipes each of which is composed of an outer pipe and an inner pipe inserted into the outer pipes are prefabricated, and thrust is applied to the outer pipes from a pipe-jacking machine so that the inner pipes and the outer pipes can be simultaneously propelled. In this pipe-jacking method, every time an individual double-wall pipe is propelled into the ground, the edge of an inner pipe of the individual double-wall pipe which has been propelled into the ground is welded with the edge of new a individual double-wall pipe which is disposed in a start vertical shaft so that a conduit comprised of inner pipes with the highest gas tightness can be laid by one pipe-jacking method.